[clang] [clang]get non-injected-class before finding instantiated decl (PR #70886)

[Henrik G. Olsson via cfe-commits]

https://github.com/hnrklssn commented:

LGTM, but I'm not very familiar with the C++ specific parts of clang, so someone else ought to take a look also

https://github.com/llvm/llvm-project/pull/70886